Year	Percent
1991	38.63
1992	38.85
1993	38.92
1994	38.92
1995	38.89
1996	39.02
1997	38.94
1998	38.73
1999	38.56
2000	38.58
2001	38.59
2002	38.52
2003	38.45
2004	41.46
2005	39.93
2006	38.44
2007	36.96
2008	35.47
2009	33.89
2010	32.42
2011	31.02
2012	29.64
2013	28.3
2014	27.04
2015	26.74
2016	26.45
2017	26.15
2018	25.85
2019	25.49